ADAM23, a member of brain MDC family, is important for the development of central nervous system. P19 mouse embryonal carcinoma cells can differentiate into neurons when cultured in aggregates and induced with retinoic acid (RA). In this study, we found under the condition without RA induction, knocking down ADAM23 by RNAi promoted neuronal differentiation, and recombinant GST-ADAM23-DIS protein can inhibit the neuronal differentiation of P19/ADAM23-Knockdown (P19/ADAM23KD) cells when without RA induction. In P19/ADAM23KD cells, there were more cells arrested in G1 phase than in normal P19 cells, which was caused by up-regulation of P57KIP2 and P27KIP1 expression. P27KIP1 was up-regulated during the differentiation process of both P19/ADAM23KD cells without RA induction and P19 cells with RA induction. Transient over-expression of P27KIP1 in P19 cells also promoted neuronal differentiation of P19 cell. All these results indicate that ADAM23 suppresses neuronal differentiation through its disintegrin domain, and Adam23 knockdown up-regulates P27KIP1 in P19/ADAM23KD cells, which is one of the reasons that P19/ADAM23KD cells can differentiate into neurons without RA induction.